The Banned IPs module is useful when you want to prevent users with certain IP addresses from accessing or using your website in a certain way. This typically happens when a user posts offensive material on a website (e.g. on a forum), harasses site members or behaves in some other unwanted way. IP banning can also be used to restrict access to your websites from certain areas of the world. These bans can be set either for individual websites or globally for all websites in the system.
To learn how to enable the Banned IPs module, please see Developer's Guide -> Modules - > Banned IPs - > Enabling IP banning.
Adding banned IPs can easily be performed by site administrators. Developer's Guide -> Modules - > Banned IPs - > Banning an IP address describes how. To find out how to determine which IP a user you want to ban is using, please see Finding an IP address in the same chapter of the Developer's Guide.
The Banned IPs internals and API sub-chapter provides information about the database tables and classes used by the module and examples of how banned IPs can be managed using the API.
IP banning is usually used as a last resort and there are other modules which can help you deal with offensive content and keep your website clean. Please refer to Developer's Guide -> Modules -> Abuse report and Developer's Guide -> Modules -> Bad words to read more.